1. Field of the Invention
This invention relates to a liquid jet recording head and device, and more particularly to a liquid jet recording head and device having a liquid heating means in a recording head.
2. Description of the Prior Art
FIG. 1 shows a schematic illustration of a liquid jet recording device of the prior art.
In this Figure, the member denoted by the numeral 101 is a head unit having a built-in liquid jet recording head, which performs recording on the paper 104 by discharging flying droplets of a liquid such as ink fed through a tube 103 from a main tank 102.
The member shown by the numeral 105 is a discharge restoration pump which is used when droplet discharging becomes incomplete or interrupted, and the pump 105 performs restoration of discharging actuation by sucking liquid from an orifice not shown within the head unit through a tube 106. During this sucking operation, the liquid within the head unit 101 is also sucked through a tube 107.
The sucked liquid is led to a waste liquor reservoir 108 to be stored therein.
The cap shown by the numeral 109 is provided for preventing the liquid within the head unit 101 from drying or from contamination by impurities such as dust when liquid jet recording is not performed over a long term or during transportation of the device, and it is fitted to the tip portion of the head unit 101.
The member designated by the numeral 110 is a carriage on which the head unit 101 is mounted, the numeral 111 showing a platen.
A liquid jet recording device having such a structure is finding wide use, since it generates less noise as compared with an impact device such as a wire dot recording device, and yet requires no post-recording treatment such as fixing.
The liquid jet recording devices of this kind may be classified into two kinds of an on-demand type and a continuous type.
The on-demand type device is a system, in which droplets are discharged only when a recording command is received, while the continuous type device is a system in which droplets are discharged continuously at a constant frequency and an electrical field applied on the space through which the droplets are flying is changed in response to the recording command, thereby changing the route of the droplets to effect recording, while recovering and circulating the droplets not concerned with recording.
The on-demand type device has the advantage of being, simpler in structure than the continuous type.
On the other hand, the liquid to be used for recording undergoes changes in physical properties such as viscosity or surface tension depending on the temperature, and the sizes of droplets discharged change depending on temperature changes, even when the same energy is generaed by an energy generating member such as piezoelectric element of the droplet forming means. As a result, the recorded dots on the recording paper are changed in size to give unstable recording quality or image quality depending on the conditions of use of the device. This is a great obstacle in obtaining recording of high quality.
For overcoming such drawback, attempts have been made to provide a means for detecting the temperature of the environment under which the device is placed or of the droplet forming means so as to compensate temperature changes by heating a part or whole of the droplet forming means through the signals sent from such a detecting means, thereby keeping constant the temperature of the droplet forming means.
FIG. 2 shows an example of the prior art having such a structure.
In the example shown in FIG. 2, the head unit 101 is constructed of a multi-orifice type having a plurality of outlets 112.
The outlets 112 are formed at the tip ends of the liquid pathways 113, each liquid pathway 113 being housed at the bottom within the liquid reservoirs 114 partitioned independently of each other.
The respective liquid reservoirs 114 are fed with liquids such as ink with the same color or different colors.
At the bottoms of the respective liquid reservoirs 114, heating means 115 in the form of a flat plate are fixed.
In the vicinity of the outlets 112 in the liquid pathways 113, energy generating members such as piezoelectric elements are mounted along the liquid pathways.
A temperature detecting means is mounted at either one of the liquid reservoirs selected to perform temperature compensation by heating with the heating means 115 to keep the liquid at a constant temperature.
In such a construction, in order that all of the plural number of droplet forming sections may be heated with uniform watt density, the portions to be heated of the respective droplet forming sections, namely the areas at the back face of the respective liquid reservoirs are made equal and the effective area on the heating surface of the heating means 115 is also made equal to the total sum of the areas of the portions to be heated of the respective droplet forming sections.
However, with such a structure as mentioned above, when the difference between the temperature controlled by temperature compensation and the environmental temperature is great, dissipation of heat from the portions other than the portions to be heated of the droplet forming sections, namely the portions at the upper faces or four side faces of the liquid reservoirs 114 which contact the air, becomes great, and the temperature of the droplet forming sections at both ends with greater areas contacting the air becomes lower than the temperature of the droplet forming selections located inside of the device.
Thus, temperature compensation cannot effectively performed which can cause marked lowering in recording quality or image quality such as different sizes of recorded dots for respective orifices.
On the other hand, in a structure as shown in FIG. 2, the tip end of the temperature sensor 117 is inserted into the liquid, and at least a part of the temperature sensor is formed of a metal, and in most cases an appropriate voltage is applied for detection of the temperature.
Also, since a dye which is an electrolyte is employed in the liquid such as ink for the purpose of coloration, there was involved the drawback that electrolytic dissolution occurs at the metal portion of the temperature sensor on prolonged usage, whereby the device can no longer be used.
Accordingly, an attempt has been made to coat the surface of the temperature sensor with a fluorine resin or the like to prevent the dissolution, but this method leads a corresponding increase in cost.
A structure as shown in FIG. 3 has been proposed for alleviating these drawbacks.
In the example shown in FIG. 3, in order to avoid electrolytic dissolution of the temperature sensor 117, an detection piece 118 is provided at the side of the head unit 101 and the temperature sensor 117 is provided on the detection piece.
The temperature sensor 117 detects the environmental temperature under which the device is set on initial actuation of the device, and gives heat quantity corresponding to this temperature to the liquid through the heater 115.
However, when such a structure is employed, since the liquid temperature is not detected directly, there is involved the drawback that accurate temperature compensation in real time is not possible.
As another drawback, the head unit 101 with a structure as shown in FIG. 2 has a projection 101a as shown in FIG. 4 and fixed by screwing onto the carriage 110 through the projection 101a.
Whereas, by employment of such a mounting structure, the heat of the heating means will escape toward the carriage 110, whereby the heat unit 101 and the carriage 110 are regarded as one body, with the disadvantageous result that it will take a long time before reaching the target control temperature even if the device may be actuated to actuate the temperature compensating circuit, thereby making the waiting time of the device longer.